In automotive applications, there is a push for energy efficiency. Efficiencies can be gained for example, by selectively deactivating cylinders in a multiple-cylinder internal combustion engine under certain engine load conditions by deactivation of one or more of the engine valves.
For an overhead-cam engine, one known approach is to provide switchable hydraulic lash adjusters that deactivate the roller finger followers (RFFs) by changing the motion of engine cams into a lost motion that is absorbed by the lash adjuster itself instead of transferring the lift motion to the associated valves. Such lash adjusters are known in the art as switchable hydraulic lash adjusters (SHLAs).
One prior art SHLA indicated at 8 in FIG. 5 includes a conventional hydraulic lash adjuster disposed in a plunger assembly having a domed head for engaging the RFF. The plunger assembly itself is slidably disposed in an inner housing containing the locking pins, which in turn is slidably disposed in an outer housing that is located in a corresponding opening in a cylinder head. The inner housing may be selectively latched and unlatched hydro-mechanically to the outer housing by the selective application of force by a spring and pressurized engine oil on the locking pins.
During engine operation in the valve deactivation mode, the locking pins are withdrawn from locking features (typically an annular groove) in the outer housing, and the inner housing is then reciprocally driven in oscillation by the socket end of the RFF which pivots on its opposite pad end on the valve stem where the valve spring acts with sufficient force so that the valve remains immobile as the cam lobe acts on the RFF. The inner housing is returned during half the lost motion reciprocal cycle by lost motion spring(s) disposed between the inner housing and the outer housing.
In this known prior art SHLA, the required lost motion spring packaging space is significantly larger than that of a non-switching HLA and so the packaging length in an engine is necessarily longer than desired. Given the space requirements, this option is often not even considered for implementation in new higher efficiency engines.
Another arrangement is disclosed in U.S. Pat. No. 8,215,276 which reduces the packaging length of the SHLA by utilizing oil pressure alone or in combination with a shorter spring located in the outer housing that presses against the bottom of the inner housing. However, this arrangement still suffers from shortcomings due to the need for a further pressurized hydraulic oil supply gallery in the engine head.
It would be desirable to provide an improved SHLA which requires less packaging length than is currently available.